1. Field of the Invention
The present invention relates to a temperature detector circuit and an oscillation frequency compensation device using it, and more particularly to a MOS-transistor-based temperature detector circuit which has stable output characteristics and an oscillation frequency compensation device including such temperature detector circuit.
2. Discussion of the Background
FIG. 1 illustrates an example of a background temperature detector circuit using a bipolar transistor with commonly connected base and collector. FIG. 2 illustrates an example of a background temperature detector circuit using a Darlington connection of bipolar transistors.
The background temperature detector circuit of FIG. 1 drives the bipolar transistor by a constant current to use a temperature dependency of forward direction voltage for temperature detection. This is of the same kind as a method of using a temperature dependency of forward direction voltage in a so-called PN junction diode. Further, a series connection of two or more of this circuit in FIG. 1 is also known.
In FIG. 2, this circuit has a configuration of Darlington connection with two or more bipolar transistors in order to raise its output sensitivity. This circuit realizes a high sensitivity temperature sensor having two or more Darlington connections and a constant current power supply to the sensor. This kind of circuit may be formed on a single substrate by using a CMOS (complementary metal oxide semiconductor) manufacture process.
FIG. 3 illustrates an example of a background temperature detector circuit having MOS (metal oxide semiconductor) transistors with commonly connected gate and drain in a state of diode connection. The background temperature detector circuit of FIG. 3 uses a temperature dependency of a MOS-transistor threshold for temperature detection. The background temperature detection circuit drives the MOS transistors by a constant current and uses a voltage between the gate and a source for temperature detection.
The temperature dependency of voltage between a gate and a source of a MOS transistor having diode connection is known to change with values of the driving constant current. Specifically, the temperature dependency of threshold is dominantly effective in a minute current domain, resulting in a negative temperature inclination of voltage between the gate and the source. However, the temperature dependency of electron mobility is dominantly effective in a domain above a certain current, resulting in a positive temperature inclination of the voltage.
As illustrated in FIG. 3, the background temperature detection circuit includes a temperature detection section 81, a constant voltage generating section 82, a constant current circuit 832, and a P-type MOS transistor 831. In the temperature detection section 81, a MOS transistor 811 has the diode connection and is driven in a minute current domain to make the temperature dependency of threshold dominantly effective. To increase output sensitivity, the temperature detection section 81 is provided with a plurality of series-connected MOS transistors 8121-812m which have diode connection.
FIG. 4 illustrates an example of a background semiconductor integrated circuit for temperature detection. This circuit includes a first circuit block 97 and a second circuit block 98. The first circuit block 97 generates a reference voltage without temperature dependency. The second circuit block 98 generates an output voltage which has a temperature dependency with a similar configuration to the first circuit block 97. An output Vs1 of the first circuit block 97 and an output Vs2 of the second circuit block 98 may be compared in this circuit. In the first circuit block 97, MOS transistors 912 and 914 having different thresholds form a current mirror circuit which outputs a voltage determined based on a difference between the thresholds of these MOS transistors 912 and 914. In the first circuit block 97, a channel conductance of the MOS transistor 912 and a MOS transistor 913 is made equivalent to a channel conductance of the transistor 914 and a MOS transistor 915. On the other hand, in the second circuit block 98, a channel conductance of MOS transistors 916 and 917 is intentionally made different from a channel conductance of MOS transistors 918 and 919.
Since the output Vs2 of the second circuit block 98 may be a reference voltage with temperature dependency, it can be used as a temperature sensing element. This reference voltage Vs2 is divided so that it can be detected at a predetermined temperature by using resistances 920 and 921 and an operational amplifier 99 that outputs an output voltage Vs3. A comparator 910 compares Vs1 and Vs3 to detect a predetermined temperature, and an output buffer 911 outputs a resultant signal.